The problem with having an extinguisher is that many are only suitable for certain types of fires. and if they are used on a fire that using the wrong type of fuel, the extinguisher can cause more problems than it might safely resolve.
I guess that if you are alerted to a fire in your, the shock might impair your ability to assess the nature of the fire, and you might pick the wrong extinguisher, or of course you may not have the right extinguisher.
In relation to the video, the important aspect is not what caused the fire, it was the speed at which it took hold. Whether more modern construction has a lower flammability than the rather old American van used in the demonstration I don't know, but who in the immediacy of the moment is going to be able to rationalise the construction details and make an informed decision about how long you may have to get out.
In the event of any uncontrolled fire in any caravan the first priority should be to get out of the van and away from the danger zone. and call the fire service. Then only if it is safe to do so tackle the fire with appropriate extinguishers.